Drilling tool

ABSTRACT

A drilling tool comprises a drill tip, a chip removal part which axially adjoins the drill tip, and a drill shank which is positioned at the end of the chip removal part. Two chip flutes extend in a helical manner over the chip removal part starting at the main cutting edges of the drill tip. The drilling tool is separated into two parts in the region of the chip removal part and consists of a base body which is connected to the drill shank as one part and an exchangeable tip made of a harder material which is connected to the drill tip as another part. The exchangeable tip is connectable to the base body in a form-fitting and/or frictional-fitting manner at an axial separation point.

FIELD OF THE INVENTION

The invention relates to a drilling tool, having a removable drill tip.Various connections between the drill shank and drill tip, as well asvarious drill tip features are discussed.

BACKGROUND OF THE INVENTION

The twist drill is the most widely used drilling tool for drilling intosolid material and bores having a diameter up to approximately 18 mm.The material used in manufacturing twist drills is alloyed tool steel,high-speed steel, and hard metal. If needed, the drill can be coatedwith a wear-reducing layer of e.g. titanium nitride. Wear occurs mainlyin the vicinity of the drill tip in the region of the main cutting edgeand at the guide chamfer. In order to eliminate the wear, it has beenhitherto known to re-grind the drill at the corresponding flanks. Inthis, it is found to be disadvantageous that the drill becomes shorterduring the grinding operation. In order to avoid this disadvantage, itis further known (DE-C-37 09 878) that the cutting part consists of abase body connected to the drill shank as one part and an exchangeabletip connected to the drill tip as one part, which are connectable toeach other in a form- and friction-fitting manner at an axial separationpoint.

Based on this, it is the object of the invention to improve the knowndrilling tool of the type described above such that a reduction of wearand an improvement of the drilling quality can be obtained by simpleproductional measures.

SUMMARY OF THE INVENTION

The invention is based on the idea that with a separation into two partsof the drill in the region of the chip removal part the drill tip can bemade of a different, harder material and easily exchanged when used tothe limit of wear. In order to achieve this, it is proposed that theexchangeable tip as a whole consists of a material which is harder thanthe base body. The exchangeable tip advantageously consists of a cuttingmaterial from a group of hard metals or ceramics and may, in this case,be made as a sintered powder injection moulded part. The exchangeabletip can also be made of a wear-resistent coated tool steel. The basebody on the other hand advantageously consists of tool steel or ahigh-speed steel.

In a preferred or alternative embodiment of the invention, the maincutting edges each have two cutting edges which are formed into theexchangeable tip, sloped against each other in a roof shape, and alignedin a generally radial direction. The cutting edges of the two maincutting edges can be positioned in equal radial distances from the drillaxis, forming a double cutter, so that they are engaged over their fulllength during the drilling operation. This is advantageous, though, onlywhen one of the two inner cutting edges overlaps with the drill axis.The cutting edge corners which protrude radially over the outercircumference of the drill tip advantageously merge into a generallyaxially aligned guide edge. The guide edge is adjoined in thecircumferential direction by a guide rib which radially protrudes overthe outer circumference and extends over part of the circumference ofthe drill tip. The peak and the outwardly protruding cutting edgecorners of the two main cutting edges are positioned in equal radialdistances from the drill axis. Accordingly, the outer cutting edges ofthe two main cutting edges are of equal length, while the inner cuttingedges are of different length. In a preferred embodiment of theinvention, the cutting edges and a plane which is perpendicular to thedrill axis include an angle of 2° to 30°, preferably of 8° to 16°, sothat the pairs of cutting edges of the main cutting edges include a roofangle of 120° to 176°, preferably of 148° to 164°.

The cutting edges formed into the exchangeable tip may be at leastpartially bevelled and/or rounded-off and possibly wave-shaped. Further,indentations, raised portions, steps, or ribs, which preferably reachthe cutting edges, can be formed into the cutting faces. It isespecially advantageous for the formation of the chips when chip forminghollows are formed into the cutting faces, which are preferablypositioned at an axial distance with respect to the cutting edges. Thechip forming hollows may have sides corresponding in shape to theroof-shape of the cutting edges at least at their sides adjoining thecutting edges. The cutting faces which are generally axially paralleland radially aligned delimit a chip space which merges into the chipflutes in the direction of chip travel.

In order to create the connection between the exchangeable tip and thebase body, the exchangeable tip is advantageously connected in one pieceto a coupling piece which protrudes over the side opposing the frontrake. The coupling piece itself has a driver which meshes with acomplementary driving part of the base body and may be fitted with ananchoring pin which protrudes centrally over the exchangeable tip andwhich can be inserted into the base body and anchored there in a form-and/or frictional-fitting manner. Advantageously, the coupling piece hastwo mutually opposed drivers which each mesh with a complementarydriving part of the base body.

In order to ensure an exact centering of the exchangeable tip on thebase body, it is of advantage when the coupling piece has at least twopartially cylindrical, convex centering sections which are positioned ordistributed over or about the circumference and which fit exactly into abushing at the base body, which has partially cylindrical, concavecentering sections which are complementary to the convex centeringsections. For the rotary drive there are provided at least two axiallyopen radial recesses, which are positioned inbetween two adjacent convexcentering sections of the coupling piece, for the engagement of a drivertooth which radially protrudes into the bushing between two adjacentconcave centering sections of the base body.

For the frictional connection between the exchangeable tip and the basebody, it is of advantage when the exchangeable tip has a plane shoulderwhich protrudes generally radially over the coupling piece. The shoulderpreferably is pressable against a plane face of the base body by meansof a clamping mechanism. The shoulder and face are preferably eachsubdivided into two areas which are separated from each other in thecircumferential direction by the flutes. A further improvement in thisrespect is attained in that the coupling piece has an end face whichprotrudes generally radially over the anchoring pin, the end face beingpressable against a bottom face which delimits the bushing.

For the creation of a form- and frictional-fitting connection betweenthe exchangeable tip and the base body, at least one generally radiallyaligned conical countersink is advantageously positioned in the couplingpiece, a threaded bolt having a conical tip, which is positioned in agenerally radial threaded bore in the base body, being engaged in aform- and friction-fitting manner in the countersink. The conicalcountersink is advantageously formed into one of the drivers of thecoupling piece, while the threaded bore penetrates one of the drivingpieces of the base body.

In a further possible connection between the exchangeable tip and thebase body, the coupling piece of the exchangeable tip has a continuouscross bore, through which a clamping screw extends, which is led througha bore of the driving part of the base body and which is screwed into athreaded bore of the opposing driving part, by which a tensioningbetween the exchangeable tip and the base body without any free play inthe axial and circumferential directions is created.

Especially in drilling tools having a very small diameter, in which amechanical connection between the exchangeable tip and the base body isdifficult, the exchangeable tip and the base body are advantageouslylaser-welded or hard-soldered to each other at their joining locationswhich are positioned between the coupling piece and the bushing.

In a further advantageous embodiment of the invention, the exchangeabletip has an axial snap-in reception which is delimited by acircumferential face and is located in the region of the separationpoint, into which a snap-in pin, which protrudes axially over acircumferential shoulder, can be inserted and locked by pressing theshoulder against the face. This ensures that the torque and retractingforces acting on the drill are taken up by the separating point.

The snap-in pin may carry a catch spring which can be snapped into atleast one radial undercut within the snap-in reception. Advantageously,the catch spring has two catch legs which radially protrude in oppositedirections of the snap-in pin slanted in the direction of the shoulder,the catch legs being engageable into the undercuts of the snap-inreception while creating an axial pre-tension. The catch legs may beconnected to each other in one piece by means of a spring pin which isconnected to the face side of the snap-in pin. The catch spring can bescrewed to the face side of the snap-in pin preferably by two screwswhich extend through two holes in the spring pin, or welded, soldered orglued to the snap-in pin in the region of the spring pin. It has provento be especially advantageous when the catch spring is welded to thesnap-in pin by means of laser welding. Additionally, the snap-in pin canhave an undercut groove for the form-fitting acception of thecomplementary deformed spring pin. In principle it is also possible todirectly form the catch legs, which are formed to be spring tongues,onto the snap-in pin.

In a further preferred embodiment of the invention the radial undercutis formed by a transverse or slanted opening which penetrates the wallof the snap-in reception, wherein the transverse or slanted openingpenetrates one of the side rakes of the exchangeable tip and the catchleg or the spring tongue can be unlocked from the outside through thecorresponding transverse or slanted opening.

For the transmission of force and torque in the region of the separationplane, it is of advantage when the snap-in reception and the snap-in pinhave a generally rectangular cross section with two mutually opposingbroad side faces and small side faces, wherein the broad side faces arelocated adjacent the outer chip surfaces within the chip removal partand the small side faces are located adjacent to the outer side rakes.

In order to save space, when the catch legs overlap the snap-in pin inthe region of its small side faces in the direction of the shoulder,pockets for the reception of the catch legs are left free between thesmall side faces of the snap-in pin and the snap-in reception. On theother hand, for the improvement of the rotary drive in the region of theseparation plane, the snap-in pin is fit into the complementary snap-inreception with its opposing, parallel aligned broad side faces. Withrespect to the slanted outwardly directed snap-in legs of the catchspring, it is of advantage, when the broad side faces have a generallytrapeze-shaped outline and that the small side faces are correspondinglypositioned in a wedge shape with respect to each other.

In order to achieve an axial friction-fit in the region of theseparation plane, the catch legs of the catch spring have a snap-in basewhich can be snapped into the undercut under radial spreading and whichare supported in the snapped-in state on a preferably slanted lockingface of the undercut. The locking face advantageously includes an angleof 5° to 15° with a radial plane which is perpendicular with respect tothe drill axis.

In principle it is possible, to form the snap-in pin and the snap-inreception rotationally symmetrical with respect to the drill axis. Inthis case at least one fitting bolt is additionally provided radiallyoutside the snap-in pin which engages in facing axially parallel fittingbores of the base body and the exchangeable tip for the transmission oftorque.

It is further possible to fix the snap-in pin in the snap-in receptionby means of at least one locking screw which extends through a threadedbore in the wall of the snap-in reception.

In an advantageous embodiment of the invention, the base body and theexchangeable tip are connectable to each other in a frictional-fittingmanner by means of a fitting pin or bolt which is made of a shape memoryalloy. The fitting pin or bolt can be screwed with its one end into anaxial threaded bore of the base body and with its other end into afitting bore of the exchangeable tip in a frictional-fitting manner.

According to an advantageous embodiment of the invention, centeringmeans are provided, which center the exchangeable tip on the base bodyin a non-rotatable manner. The centering means can have at least onecentering cam which is positioned in the snap-in reception and whichengages in an open-edged opening of the snap-in pin, or at least onefitting bolt which bridges the separating point and which engages inaligned fitting bores of the exchangeable tip and base body.

In order to improve the drilling result, at least one coolant bore whichpenetrates the base body and the exchangeable tip axially or in a spiralmanner and which bridges the separating point may be provided.

In order to reduce the amount of stock, a base body having a given outerdiameter may be fitted with exchangeable tips which have differing outerdiameters.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is further described with the aid ofembodiments schematically shown in the drawing, in which

FIG. 1a shows a side view of a drilling tool having an exchangeable tipin an exploded view;

FIG. 1b shows a perspective view of the exchangeable tip of FIG. 1.

FIG. 1c shows a different perspective view of the exchangeable tip ofFIG. 1;

FIG. 1d shows another perspective view of the exchangeable tip of FIG.1;

FIG. 1e shows yet another different perspective view of the exchangeabletip of FIG. 1;

FIG. 1f shows an enlarged section of the base body of the drilling toolaccording to FIG. 1a;

FIG. 2 shows an embodiment of an exchangeable tip modified with respectto FIG. 1 in a perspective view corresponding to FIG. 1d;

FIG. 3a shows a further modified embodiment of an exchangeable tip in aperspective view;

FIG. 3b shows a different perspective view of the exchangeable tip inFIG. 3a;

FIG. 3c shows a section of the base body for the exchangeable tip ofFIG. 3a and b;

FIG. 4a shows an exploded view of a further modified embodiment of adrilling tool having an exchangeable tip;

FIG. 4b shows a front face view of the base body of the drilling tool ofFIG. 4a;

FIG. 5a shows a side view of a twist drill having an exchangeable tip;

FIG. 5b shows a top view of the drill tip in a representation enlargedwith respect to FIG. 1a;

FIG. 6 shows a section through the separation point of the twist drillhaving a first coupling variant;

FIG. 7 shows a section through the separation point of the twist drillhaving a second coupling variant;

FIG. 8 shows a section through the separation point of the twist drillhaving a third coupling variant;

FIG. 9a shows an axial section through the separation point of the twistdrill having a fourth coupling variant;

Fig. 9b shows a radial section through the separation point of the twistdrill having a fourth coupling variant;

FIG. 10 shows an axial section through the separation point of the twistdrill having a fifth coupling variant.

DETAILED DESCRIPTION

The drilling tools shown in the drawing are divided into two parts at aseparation point 30 and consist of a base body 32 which carries a drillshank 14 and an exchangeable tip 34 which carries a drill tip 10, whichare connectable to each other in a form- and frictional-fitting manner(FIGS. 1 to 9) or only in a frictional-fitting manner (FIG. 10) at theseparation point 30. While the base body 32 is made of tool steel or ahigh-speed steel, the exchangeable tip in its entirety is a form partmade of a cutting material selected from the group of hard metals orceramics, which is manufactured as a sintered powder injection mouldedpart. In principle it is also possible to manufacture the exchangeabletip of a tool steel which is coated with a wear-resistant material.

The drilling tool shown in FIGS. 1 to 4 has a drill tip 10, a chipremoval part 12 which follows the drill tip and which is possibly formedto be a cutting part, and a drill shank 14 which is formed to the rearof the chip removal part. The drill tip 10 has two main cutting edges 16and two front rakes 20 adjacent to the main cutting edges. Two helicalflutes 22 extend from the main cutting edges 20 of the drill tip 10 overthe chip removal part 12 up to the drill shank. The separation point 30is located in the region of the chip removal part 12.

The main cutting edges 16 each have two cutting edges 16', 16" which areformed into the exchangeable tip 34, pairs of which are positioned in aroof shape with respect to each other, and which are generally radiallyaligned. The cutting edges 16', 16" form double cutters and arepositioned at the same radial distance with respect to the drill axis78. As can be seen especially from FIG. 1b and d, only one of the innercutting edges 16' overlaps the drill axis 78, while the other innercutting edge 16' is excentrically adjacent to a step 80. The peak 82 ofthe roof and the outwardly protruding cutting edge corners 84 of the twomain cutting edges 16 are positioned at the same radial distances fromthe drill axis. The outer cutting edges 16" are therefore of equallength and the inner cutting edges 16' of different length. The pairs ofcutting edges 16', 16" include roof angles of 148° to 164° at the peak.They ensure that the drill tip is centered in the bore during drillingand does not run out.

The cutting edge corners 84 which radially protrude over thecircumference of the drill tip merge into a guide edge 86, adjoiningwhich is a guide rib 88 which extends over part of the circumference ofthe drill tip 10 and which protrudes radially over the circumference.

The flutes 22 which begin immediately beyond the main cutting edges 16in the direction of chip travel are delimited by the cutting face 90 atthe side of the cutting edges 16', 16". In the case of FIG. 1a to FIG.1e, chip forming hollows 92 are formed spaced with respect to thecutting edges 16', 16". The cutting edge sided borders have a shape thatconforms with the roof shape of the cutting edges 16', 16" . In theembodiment shown in FIG. 2 a plurality of indentations 94 whichpenetrate the cutting edges 16', 16" are provided in place of the chipforming hollows.

The exchangeable tip has a coupling piece 96 at its side opposing thefront rakes 20, which has a rotary driver 100 which meshes with acomplementary centering and driving part 98 of the base body 32. In theembodiments of FIGS. 1 and 2 there is additionally provided an axiallyprotruding anchoring pin 104 which is insertable into a mounting bore102 of the base body 32 and which can be anchored there in a form- andfriction-fitting manner.

The driver 100 has four partially cylindrical convex centering sections106 which are spaced from one another circumferentially, which fitexactly in a bushing 108 of the base body with partially cylindricalconcave centering sections 110 which are complementary to the centeringsections 106. The rotary drive is effected by way of the flanks of theaxially open radial recesses 112 each of which is positioned between twoconvex centering sections 106. A driver tooth 114 engages in each of theradial recesses 112, which protrudes radially into the bushing 108between two adjacent concave centering sections 110 of the base body 32.

The exchangeable tip has a plane shoulder 36 protruding radially overthe coupling piece 96, which is pressable against a plane face 40 of thebase body 32 by way of a clamping mechanism acting on the anchoring pin104 (FIGS. 1 and 2) or the coupling piece 96 (FIGS. 3 and 4). Theshoulder 36 and face 40 are each divided into two areas 36', 36" and40', 40" which are separated from each other in the circumferentialdirection by the flutes 22.

The clamping mechanism has a clamping screw 130 shown in examplaryfashion in FIG. 4a. In the embodiments shown in FIGS. 1 to 3, theclamping screw is positioned in a threaded bore 120, 120' of the basebody 32 and engages in an excentric conical countersink 122, 122' of theexchangeable tip with a conical tip. In the embodiment of FIGS. 1 and 2,the conical countersink 122 is positioned in the anchoring pin 104 whichis located in the mounting bore 102, while in the embodiment of FIGS. 3ato c the conical countersink 122' is positioned in the region of one ofthe radial recesses 112 of the coupling piece, whereas the bore 122'penetrates the wall in the region of one of the driver teeth 114.

In the embodiment of FIG. 4a and FIG. 4b the coupling piece 96 of theexchangeable tip 34 has a continuous cross bore 132, through which asink-head screw 130, which is led through a continuous countersunk bore134 in a driver part 98, 114 of the base body and which is screwed intoa threaded bore 136 of the diametrically opposed driver part 98, 114,penetrates between the exchangeable tip 34 and the base body 32 whilecreating play-free tension in the axial direction in the region of thefaces 36, 40 and in the circumferential direction in the region of themating flanks 138, 140 of the driver 100 and the driver parts 98.

The coupling piece 96 further has an end face 116 which faces the bottomface 118 of the bushing 108.

The twist drill shown in FIGS. 5a and b has a drill tip 10, a cuttingportion 12 following the drill tip, and a drill shank 14 which is formedto the rear of the cutting portion. The drill tip has two main cuttingedges 16, a chisel edge 18 which connects the main cutting edges at thetip, and two front rakes 20 adjacent to the main cutting edges and thechisel edge. Two helical flutes 22, which are delimited laterally by aminor cutting edge 24 with an adjoining guide chamfer 26 as well as by aside rake 28, extend from the main cutting edges 20 in the drill tip 10over the cutting portion 12.

The twist drill is divided into two parts at a separation point 30 inthe region of the cutting portion 12 and consists of a base body 32carrying the drill shank 14 and an exchangeable tip 34 carrying thedrill tip 10.

A variety of coupling means in the region of the separation point 30 areshown in FIGS. 6 to 10. In the embodiments of FIGS. 6 to 9 the base body32 has a snap-in pin 38 which protrudes over a circumferential shoulder36. The snap-in pin 38 can be snapped into an axial snap-in reception 42of the exchangeable tip 34, which is delimited by a circumferential face40, while pressing the shoulder 36 against the face 40. The snap-in pin38 carries a catch spring 44, which can be snapped into two radialundercuts 48 in the snap-in reception 42 with its catch legs 46 whichradially extend slanted in the direction of the shoulder 36. The radialundercuts 48 are formed to be slanted openings in the wall 50 of thesnap-in reception 42, through which the catch legs 46 can be unlockedfrom the outside. The catch legs 46 have a snap-in base 53 which can besnapped into the undercuts 48 under radial spreading and which isaxially supportable under tension in the snapped-in state on a slantedlocking face 52. The locking face 52 and a radial plane 54 which isperpendicular to the drill axis include an angle β of 5° to 15°.

In the embodiments of FIGS. 6 to 8 the two catch legs 46 are connectedto each other as one part by means of spring pin 56 which is connectedto the front of the snap-in pin 38. In the embodiment of FIG. 6 thecatch spring 44 is welded, soldered or glued with its spring pin 56 tothe front face of the snap-in pin 38, whereas in the embodiment of FIG.7 it is screwed to the snap-in pin 38 by means of two screws 58. In FIG.8 the snap-in pin has an undercut groove 60 for the form-fittingreception of the complementary deformed spring pin 56.

In the embodiment of FIG. 9a the catch legs 46 are formed onto thesnap-in pin 38 in the form of spring tongues.

As can be seen from the section of FIG. 9b, the snap-in reception 42 andthe snap-in pin 38 have a generally rectangular cross section oroutline, wherein two mutually opposing broad side faces 62 and smallside faces 64 are formed. The broad side faces 62 each adjoin one of theouter flutes 22 within the cutting portion and the small side faces 64each adjoin one of the outer side rakes 28. The rotary drive between thebase body 32 and the exchangeable tip 34 is effected mainly by way ofthe plane-parallel broad side faces 62, with which the snap-in pin 38 isfitted into the complementary snap-in recess. Suitable centering meansare provided for centering the exchangeable tip 34 on the base body 32,which, in the embodiment of FIG. 9b, are formed by two centering cams178 which have a semi-circular cross section. The centering cams 178engage in corresponding open-edged openings 180 in the broad side faces62 of the snap-in pin 38. In the embodiment of FIG. 9b two coolant bores66 are additionally provided, which are aligned in pairs at theseparation point 30.

In the embodiment shown in FIG. 10 the base body 32 has a threaded bore68 which is open toward the separation point 30, and the exchangeabletip 34 has a fitting bore 70 which is aligned with the threaded bore 68.A bolt 72 is screwed into the threaded bore 68 with its threaded part74, which engages with its thread-free part 76 in the fitting bore 70 ofthe exchangeable tip 34 in a friction-fitting manner. The bolt 72consists of a shape memory alloy. It is fitted into the fitting bore 70at a low temperature and expands in the bore at room temperature tocreate a friction-fitting connection.

I claim:
 1. A drilling tool, comprising a drill tip having two maincutting edges positioned at approximately equal circumferentialdistances from each other, and two cutting faces and front rakesadjoining the main cutting edges, a chip removal part axially adjoiningthe drill tip and formed as a cutting part, a drill shank positioned atan end of the chip removal part opposing the drill tip, and two chipflutes which extend in a helical manner over the chip removal partstarting at the main cutting edges of the drill tip, the chip removalpart comprising a base body connected to the drill shank as one part andan exchangeable tip connected to the drill tip as another part, whichare connectable to each other in a form-fitting or frictional-fittingmanner at an axial separation point, the exchangeable tip as a wholecomprising a material harder than the base body, the exchangeable tipconnecting in one piece to a coupling piece protruding over the sideopposing the front rake, the coupling piece having a driver for meshingwith a complementary driving part of the base body, the coupling piecehaving an anchoring pin protruding centrally over the exchangeable tipand insertable into the base body for anchoring therein in aform-fitting or frictional-fitting manner, the coupling piece having atleast two partially cylindrical, convex centering sections positionedabout the circumference and which fit into a bushing at the base bodyhaving partially cylindrical, concave centering sections complementaryto the convex centering sections.
 2. A drilling tool, comprising a drilltip having two main cutting edges positioned at approximately equalcircumferential distances from each other, and two cutting faces andfront rakes adjoining the main cutting edges, a chip removal partaxially adjoining the drill tip and formed as a cutting part, a drillshank positioned at an end of the chip removal part opposing the drilltip, and two chip flutes which extend in a helical manner over the chipremoval part starting at the main cutting edges of the drill tip, thechip removal part comprising a base body connected to the drill shank asone part and an exchangeable tip connected to the drill tip as anotherpart, which are connectable to each other in a form-fitting orfrictional-fitting manner at an axial separation point, the exchangeabletip as a whole comprising a material harder than the base body, theexchangeable tip connecting in one piece to a coupling piece protrudingover the side opposing the front rake, and the coupling piece having atleast two partially cylindrical, convex centering sections positionedabout the circumference and which fit into a bushing at the base bodyhaving partially cylindrical, concave centering sections complementaryto the convex centering sections.
 3. The drilling tool of claim 1,wherein at least one axially open radial recess is positioned inbetweentwo adjacent ones of the convex centering sections of the coupling piecefor the engagement of a driver tooth radially protruding into thebushing between two adjacent ones of the concave centering sections ofthe base body.
 4. A drilling tool, comprising a drill tip having twomain cutting edges positioned at approximately equal circumferentialdistances from each other, and two cutting faces and front rakesadjoining the main cutting edges, a chip removal part axially adjoiningthe drill tip and formed as a cutting part, a drill shank positioned atan end of the chip removal part opposing the drill tip, and two chipflutes which extend in a helical manner over the chip removal partstarting at the main cutting edges of the drill tip, the chip removalpart comprising a base body connected to the drill shank as one part andan exchangeable tip connected to the drill tip as another part, whichare connectable to each other in a form-fitting or frictional-fittingmanner at an axial separation point, the exchangeable tip as a wholecomprising a material harder than the base body, the exchangeable tipconnecting in one piece to a coupling piece protruding over the sideopposing the front rake, the coupling piece having a driver for meshingwith a complementary driving part of the base body, the coupling piecehaving an anchoring pin protruding centrally over the exchangeable tipand insertable into the base body for anchoring therein in aform-fitting or frictional-fitting manner, the exchangeable tipincluding a plane shoulder protruding generally radially over thecoupling piece, and the shoulder being pressable against a plane face ofthe base body by means of a clamping mechanism.
 5. The drilling tool ofclaim 4, wherein the shoulder and the plane face are each subdividedinto two areas separated from each other in the circumferentialdirection by the flutes.
 6. The drilling tool of claim 1, wherein atleast one generally radially aligned conical countersink is positionedin the coupling piece, and a threaded bolt having a conical tip ispositioned in a generally radial threaded bore in the base body forengagement in a form-fitting and friction-fitting manner in thecountersink.
 7. The drilling tool of claim 6, the driver comprising oneof a plurality of drivers, and wherein the conical countersink is formedinto one of the drivers of the coupling piece, and the threaded borepenetrates one of a plurality of driving pieces of the base body.
 8. Thedrilling tool of claim 1, the driving part comprising one of a pluralityof opposing driving parts, and wherein the coupling piece of theexchangeable tip has a continuous cross bore, through which a clampingscrew extends, which is led through a bore of the driving part of thebase body and which is screwed into a threaded bore of the opposingdriving part, by which a tensioning between the exchangeable tip and thebase body without any free play in the axial and circumferentialdirections is created.
 9. A drilling tool, comprising a drill tip havingtwo main cutting edges positioned at approximately equal circumferentialdistances from each other, and two cutting faces and front rakesadjoining the main cutting edges, a chip removal part axially adjoiningthe drill tip and formed as a cutting part, a drill shank positioned atan end of the chip removal part opposing the drill tip, and two chipflutes which extend in a helical manner over the chip removal partstarting at the main cutting edges of the drill tip, the chip removalpart comprising a base body connected to the drill shank as one part andan exchangeable tip connected to the drill tip as another part, whichare connectable to each other in a form-fitting or frictional-fittingmanner at an axial separation point, the exchangeable tip as a wholecomprising a material harder than the base body, the exchangeable tipconnecting in one piece to a coupling piece protruding over the sideopposing the front rake, the coupling piece having a driver for meshingwith a complementary driving part of the base body, the coupling piecehaving an anchoring pin protruding centrally over the exchangeable tipand insertable into the base body for anchoring therein in aform-fitting or frictional-fitting manner, wherein the coupling piecehas an end face protruding generally radially over the anchoring pin,and the end face being pressable against a bottom face delimiting abushing.
 10. The drilling tool of claim 1, wherein the exchangeable tipand the base body are laser-welded or hard-soldered to each other attheir joining locations which are positioned between the coupling pieceand the bushing.
 11. The drilling tool of claim 1, wherein a coolantbore penetrates the base body and the exchangeable tip and bridges theseparating point.
 12. The drilling tool of claim 1, wherein the basebody and the exchangeable tip have outer diameters which differ from oneanother.
 13. The drilling tool of claim 1, wherein the material of theexchangeable tip comprises a cutting material from a group of hardmetals, ceramics or tribologically-resistent coated tool steels.
 14. Thedrilling tool of claim 1, wherein the exchangeable tip is formed as asintered powder injection moulding part.
 15. The drilling tool of claim1, wherein the base body comprises tool steel or a high-speed steel. 16.The drilling tool of claim 1, wherein the main cutting edges each havetwo cutting edges formed into the exchangeable tip, sloped against eachother in a roof shape, and aligned in a generally radial direction. 17.The drilling tool of claim 16, wherein the cutting edges of the two maincutting edges are positioned in equal radial distances from a drillaxis, forming a double cutter.
 18. The drilling tool of claim 16, thetwo cutting edges of each of the main cutting edges comprising an innercutting edge and an outer cutting edge, and wherein only one of the twoinner cutting edges overlaps with a drill axis.
 19. The drilling tool ofclaim 16, wherein cutting edge corners of the cutting edges protruderadially over an outer circumference of the drill tip and merge intogenerally axially aligned guide edges.
 20. The drilling tool of claim19, wherein a guide rib radially protrudes over the outer circumferenceand extends over part of the circumference of the drill tip and adjoinsthe guide edge in a circumferential direction.
 21. The drilling tool ofclaim 16, wherein a peak and outwardly protruding cutting edge cornersof the two main cutting edges are positioned in equal radial distancesfrom a drill axis.
 22. The drilling tool of claim 16, the two cuttingedges of the two main cutting edges comprising respective inner andouter cutting edges, and wherein the outer cutting edges are of equallength and the inner cutting edges are of different length.
 23. Thedrilling tool of claim 16, wherein the cutting edges and a plane whichis perpendicular to a drill axis include an angle of 2° to 30°.
 24. Thedrilling tool of claim 16, wherein the pairs of cutting edges of themain cutting edges include a roof angle of 120° to 176°.
 25. Thedrilling tool of claim 16, wherein the cutting edges are wave-shaped.26. The drilling tool of claim 16, wherein indentations, raisedportions, steps, or ribs, which reach the cutting edges, are formed intothe cutting faces.
 27. The drilling tool of claim 16, wherein thecutting edges are at least partially bevelled or rounded-off.
 28. Thedrilling tool of claim 1, wherein the exchangeable tip is formed as ahelical drill tip having a chisel edge.
 29. The drilling tool of claim16, wherein chip forming hollows are formed into the cutting facespositioned at an axial distance with respect to the cutting edges. 30.The drilling tool of claim 29, wherein the chip forming hollows havesides corresponding in shape to the roof-shape of the cutting edges atleast at sides adjoining the cutting edges.
 31. The drilling tool ofclaim 1, wherein the cutting faces which are generally axially paralleland radially aligned delimit a chip space which merges into the chipflutes in a direction of chip travel.
 32. The drilling tool of claim 1,wherein the exchangeable tip includes at least one coolant bore which isgenerally axially parallel and exists in a region of the front rakes.33. The drilling tool of claim 2, wherein at least one axially openradial recess is positioned inbetween two adjacent ones of the convexcentering sections of the coupling piece for the-engagement of a drivertooth radially protruding into the bushing between two adjacent ones ofthe concave centering sections of the base body.
 34. The drilling toolof claim 2, wherein the exchangeable tip includes a plane shoulderprotruding generally radially over the coupling piece, the shoulderbeing pressable against a plane face of the base body by means of aclamping mechanism.
 35. The drilling tool of claim 34, wherein theshoulder and the plane face are each subdivided into two areas separatedfrom each other in the circumferential direction by the flutes.
 36. Thedrilling tool of claim 2, wherein at least one generally radiallyaligned conical countersink is positioned in the coupling piece, and athreaded bolt having a conical tip is positioned in a generally radialthreaded bore in the base body for engagement in a form-fitting andfriction-fitting manner in the countersink.
 37. The drilling tool ofclaim 2, the driver comprising one of a plurality of drivers, andwherein the conical countersink is formed into one of the drivers of thecoupling piece, and the threaded bore penetrates one of the drivingpieces of the base body.
 38. The drilling tool of claim 2, the drivingpart comprising one of a plurality of opposing driving parts, andwherein the coupling piece of the exchangeable tip has a continuouscross bore, through which a clamping screw extends, which is led througha bore of the driving part, of the base body and which is screwed into athreaded bore of the opposing driving part, by which a tensioningbetween the exchangeable tip and the base body without any free play inthe axial and circumferential directions is created.
 39. The drillingtool of claim 2, wherein the coupling piece has an end face pressableagainst a bottom face delimiting the bushing.
 40. The drilling tool ofclaim 2, wherein the exchangeable tip and the base body are laser-weldedor hard-soldered to each other at their joining locations which arepositioned between the coupling piece and the bushing.
 41. The drillingtool claim 2, wherein a coolant bore penetrates the base body and theexchangeable tip and bridges the separating point.
 42. The drilling toolclaim 2, wherein the base body and the exchangeable tip have outerdiameters which differ from one another.
 43. The drilling tool of claim2, wherein the material of the exchangeable tip comprises a cuttingmaterial from a group of hard metals, ceramics ortribologically-resistent coated tool steels.
 44. The drilling tool ofclaim 2, wherein the exchangeable tip is formed as a sintered powderinjection moulding part.
 45. The drilling tool of claim 2, wherein thebase body comprises tool steel or a high-speed steel.
 46. The drillingtool of claim 2, wherein the main cutting edges each have two cuttingedges formed into the exchangeable tip, sloped against each other in aroof shape, and aligned in a generally radial direction.
 47. Thedrilling tool of claim 46, wherein the cutting edges of the two maincutting edges are positioned in equal radial distances from a drillaxis, forming a double cutter.
 48. The drilling tool of claim 46, thetwo cutting edges of each of the main cutting edges comprising an innercutting edge and an outer cutting edge and wherein only one of the twoinner cutting edges overlaps with a drill axis.
 49. The drilling tool ofclaim 46, wherein cutting edge corners of the cutting edges protruderadially over an outer circumference of the drill tip and merge intogenerally axially aligned guide edges.
 50. The drilling tool of claim49, wherein a guide rib radially protrudes over the outer circumferenceand extends over part of the circumference of the drill tip and adjoinsthe guide edge in a circumferential direction.
 51. The drilling tool ofclaim 46, wherein a peak and outwardly protruding cutting edge cornersof the two main cutting edges are positioned in equal radial distancesfrom a drill axis.
 52. The drilling tool of claim 46, the two cuttingedges of the two main cutting edges comprising respective inner andouter cutting edges and wherein the outer cutting edges are of equallength and the inner cutting edges are of different length.
 53. Thedrilling tool of claim 46, wherein the cutting edges and a plane whichis perpendicular to a drill axis include an angle of 2° to 30°.
 54. Thedrilling tool of claim 46, wherein the cutting edges are wave-shaped.55. The drilling tool of claim 46 , wherein indentations, raisedportions, steps, or ribs, which reach the cutting edges, are formed intothe cutting faces.
 56. The drilling tool of claim 46, wherein chipforming hollows are formed into the cutting faces positioned at an axialdistance with respect to the cutting edges.
 57. The drilling tool ofclaim 56, wherein the chip forming hollows have sides corresponding inshape to the roof-shape of the cutting edges at least at sides adjoiningthe cutting edges.
 58. The drilling tool of claim 2, wherein thecoupling piece includes an anchoring pin protruding centrally over theexchangeable tip and insertable into the base body for anchoringtherein, wherein the coupling piece has an end face protruding generallyradially over the anchoring pin, the end face being pressable against abottom face delimiting the bushing.